Method of manufacturing paper pulp



Patented Mar. 21, 1933 UNITED STATES ALFRED M. THOMSEN, OF SAN FRANCISCO, CALIFORNIA METHOD OF MANUFACTURING PAPER PULP No Drawing.

The object of my invention is not only to get a stronger fibre than that produced from such trees, grasses, and other substances, as are now utilized in the manufacture of paper pulp, but principally to use such substances as do not produce good pulp by existing processes. Such materials are: Saw-mill wastes of all description, mixtures of woods, sugarcane bagasse, corn-stalks, barks, and a great series of trees, for example redwood, which do not yield commercial pulp by means now available.

In general, such substances are resolved into fibres by either an acid or an alkali meth- 0d. In the former, the active substance employed is sulphur dioxide in combination with some base or mixtures of bases; in the latter, the active substance is either caustic soda or a mixture of caustic soda and sodium sulphide.

tive agent is not employed at present although it is far superior to caustic soda or any admixture of the same. The reason for this anomaly is purely economic. Any proc- 2 ess using a sodium salt as a cooking medium must be regenerative, e. g., the soda salt must be reclaimed in such form that it may be used again, otherwise the method becomes too expensive.

In the present Sulphate and Kraft processes, sulphate of soda is used as the source of alkali. In the process of reclamation it is converted into a mixture of carbonate and sulphide, and as the carbonate is inactive in the cooking it is converted into the activecaustic soda by causticizin the green liquor, e. g., a mixture of car onate, sulphide, and sulphate of sodium in solution, by means of lime. The cooking liquor of both 40 processes, therefore becomes a mixture of caustic soda and sodium sulphide.

In my improved method I use as the active agent only sodium sulphide, and as the car bonate formed during each passage of the 4 alkali through the cooking and reclamation Sodium sulphide as the sole ac- Application filed December 11, 1928. Serial No. 325,398.

phases would soon swamp the active reagent in inert material I separate the excess carbonate from the green liquor by crystallization and the constant removal of these crystals. My cooking alkali therefore becomes a mixture of carbonate, sulphide, and sulphate, to which I constantly add sulphate to make good all losses, and from which I constantly remove the excess of sodium carbonate produced.

My process, therefore, consists of the following steps n (a) Digesting the material containing fibre with a solution containing as alkali a mixture of carbonate, sulphate, and sulphide of 'sodi- '60 um;

(b) Separating the spent solution from the pulp; Y

c) Evaporating the solution;

(13) Adding sulphate of sodium;

e) Incinerating the mixed organic and mineral contents of said solution, the latter remaining as ashes;

(f) Dissolving these ashes, which are a mixture of carbonate, sulphide, and sulphate of sodium, and removing the excess carbonate, thus obtaining again a liquor of the same composition as used in (a).

I claim 1. In the process of manufacturin paper pulp, the method of liberating the fibre by cooking with a liquor containing sodium sulphide as the sole active agent, and separating the fibre from the spent cooking liquor, evaporating said liquor to a syrupy consis- 90 tency, incinerating it in a reducing atmosphere, dissolving the ashes in water, separating sodium carbonate formed during incinerating by fractional crystallization, and using the resultant mother liquor for making up fresh cooking liquor.

2. In the process of manufacturin paper pulp, the method of liberating the bre by cooking with a liquor containing sodium sulphide as the sole active agent, and separat- 9 ing the fibre from the spent cooking liquor, evaporating said liquor to a syrupy consistency, adding sodium sulphate, incinerating it in a reducing atmosphere, dissolving the 5 ashes in Water, separating sodium carbonate formed during inoinerating by fractional crystallization, and using the resultant mother liquor for making up fresh cooking liquor. In testimony whereof, I have hereunto set my signature.

ALFRED M. THOMSEN. 

